Reflecting bore sight



y 1949- H. o. JOHNSON 2,475,618

REFLECTING BORE SIGHT 2 Sheets-Sheet 1 Filed Feb. 11, 1947 Harold: D. Juhn scln July 12, 1949. O JOHNSON 2,475,618

REFLECTINQ BORE SIGHT Filed Feb. 11, 1947 2 Sheets-Sheet 2 A5 :1 fig 2/ Mi a M 23 HElTEflEf El. J 0111-15011 Patented July 12, 1949 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

In firing director-controlled guns at aircraft or other moving targets, it is necessary that the director and gun be initially oriented with respect to a predetermined or known base line, which may be a horizontal line from the director through the vertical or train axis of the gun. The director, when properly operated, affords continuously changing output values. These values include a train angle and an elevation angle. Each angle is with respect to the aforesaid base line and, of course, the gun must be initially adjusted so that its indicated angles of train and elevation are with respect to the aforesaid base line for successful engagement of enemy targets.

During firing, the gun may change its initial position materially because of subsidence of the supporting ground, recoil, and shocks, so that frequent checking is required in order to make certain that the initial adjustment is maintained. This checking is done by bore sighting the gun upon a pro-selected aiming point remote from and fixed relatively to the gun emplacement. Such a point may be a remote tree, post or specially-erected target. When such a point is selected and identified, the director, with all clutches disconnect-ed, is moved so that its sights are upon the selected point. The gun is also adjusted so that the axis of its bore passes through the selected point, after which the switches connecting the director with the gun are closed so that the gun is properly trained and elevated thereafter so long as the lower carriage remains in initial position.

Previous bore sighting devices for antiaircraft guns of the type discussed, required extensive manipulation of the gun such as removal of the back plate, lock frame and driving rod assemblies. These manipulations required the expenditure of much time and frequently created dangerous situations because of inability to ready the gun in time to meet an attack. Furthermore, because of the time required to perform a check there was a tendency on the part of the gun crews to delay such checks until inaccurate shooting made it apparent that r e-orientation was necessary. As a result, engagements were frequently lost and valuable ammunition wasted.

It is accordingly a prime object of this invention to provide a bore sight enabling orientation to be checked without putting the gun out of action.

A further object is to provide a bore sight that can be quickly applied and removed in a matter of seconds, while the director is being adjusted and moved to pick up a target.

Another object is to provide a bore sight whose removal will leave the gun primed and ready for the insertion of a clip of ammunition.

A still further object is to provide a bore sight that is relatively simple andeasy to construct from standard and easily-procured materials; and in general it is the object of my invention to provide a bore sight of the aforesaid characteristics that will encourage frequent orientation with consequent greater average accuracy of fire and saving of time and ammunition.

Other objects and advantages will become apparent after study of the following disclosure.

In the drawings:

Fig. 1 is an elevation, partly in section, of the breech portion of a 3'7 mm. antiaircraft directorcontrolled gun with my bore sight in position.

Fig. 2 is a perspective view of the sight.

Fig. 3 is a plan showing the reflection of the cross wires in the mirror.

Fig. 4 is .a section on an enlarged scale of the rear portion of the sight showing the mirror and its mounting, and taken upon the line 4-4 of Fig.3.

Fig. 5 is a section through a shell casing forming a portion of my invention, taken substantially upon the line 55 of Fig. 4, and showing the cross wires and aiming aperture.

Fig. 6 is a development of the mirror housing or holder of the sight.

Fig. 7 is a development of the handle portion of the sight.

Fig. 8 is a section on an enlarged scale, taken upon the line 88, Fig. 5, and showing the attachment of the cross wires to the central peep sigh-t.

Fig. 9 is an enlarged sectional detail view on a plane indicated by line 99, Fig. 5, showing a preferred manner of securing the outer ends of the cross wires flush with the shell casing.

Referring in detail to the drawings, and particularly to Fig. l, the numeral l identifies the barrel of a standard 37 mm. automatic gun having a reduced threaded breech portion 2 engaging a threaded opening in the breech extension 3. Extension 3 is connected at its lower end with recuperator piston rod 4 having a piston not shown, within recuperator cy1inder 5. The mechanism for feeding shells into the breech and ex- 3 tracting the empty casings therefrom, is contained within feed box 6 mounted on top of the trunnion block I. The =breech block 8 is shown in its lower or loading position of translation laterally of the barrel.

The supporting or barrel-engaging portion 9 of the sight may conveniently comprise an empty cartridge casing with its reduced forward portion out off, as shown upon Figs. 1, 2 and 3. The ejector flange IU of the casing is ground off flush with the bottom of the casing groove l I, to form diametrically-opposite flats, as indicated at I2 and I3, Fig. 5. While an empty cartridge casing is shown and forms a very convenient and handy support, it will be understood that a speciallyformed cylindrical shell of diameter to have a smooth fit in the breech, may be substituted, and is preferably employed where the sight is manufactured in quantities. The head of the casing is drilled, to form an enlarged central aperture about 1 inch in diameter, as indicated at M, Fig. 4.

The peep sight unit, indicated generally at l5, Figs. 4 and 8, may conveniently consist of a disc l6 having a central sighting opening. Four equally-spaced radial channels are struck in the periphery of the disc, in each of which the inner end of respective cross wires l8, are secured, as by soldering. The outer ends of the cross wires,

are attached to the shell casing as illustrated in Fig. 9. The ends pass through holes in the casing and the protruding ends are bent over to lie in channels ground in the casing and intersecting the respective holes. The bent end I9 is then soldered, as at 31, and ground off flush with the casing surface. Wires l8 may be of ZO-gauge copper. As shown upon Fig. 4, the unit is positioned in a plane normal to the axis of the shell a little forwardly of the rear end.

A mirror support or casing is indicated generally by the numeral 2!! and, in the model shown, is made from 23-gage sheet metal. The metal is first cut to shape as shown at Fig. 6, and slits 2| and 22 are cut or stamped parallel with an adjacent edge, as shown. stamped or cut to define two pairs of lugs 23 and 24. Considering lines such as X and Y, Fig. 6, extending from the end of each slit 2| and 22, at 45 thereto, the uncut, aligned base lines of each pair of lugs is spaced from such lines by the thickness of a mirror 25 plus a backing sheet 26, of cardboard or the like. The lugs are bent upwardly, at right angles to the surface of the metal sheet, after which the inclined plate or portion 21 is bent upwardly along the dotted line a, substantially at 45. The sheet is then bent along the remaining dotted lines, to form a parallelopiped having one end closed by portion 28. The meeting edges are secured together as by welding or soldering, after which the inclined portion 21, is secured to the side walls along lines X and Y, also by welding or soldering. This portion, then, forms a backing for mirror 25 and sheet 26, while lugs 23 and 24 engage the top surface of the mirror and act to hold it in position. In the model shown, a mirror i in thickness "and 1 x 1 /4 insize, wasused.

A handle 29' is formed from sheet metal cut to shape as shown upon Fig. 7 and bent along the dotted lines shown. The projecting end portions 30- and 3 i' are then welded or soldered to the sides of the mirror holder as shown at Figs. 2 and 4. The three end edges of holder 20 are secured to and within the confines of the end of flange In in In addition, the sheet is such position that the sides are parallel to the flat ground surfaces l2 and I3. The plane of mirror 25 is thus at 45 to the axis of easing 9 and to the bore of the gun when the casing is in position Within the breech thereof.

While tube 9 is shown as a shell casing, it may be specially formed of spring brass. It may be slightly tapered, if found desirable, to provide a close fit within the gun barrel. The interior should be blackened to avoid unnecessary glare. The lugs 23 and 24 should have a resiliency acting downwardly, to hold mirror 25 firmly against backing sheet 26.

Operation A previously stated, the model illustrated is shown in use with a 37 mm. automatic gun and its use will be described in connection with such gun. The gun tube is lowered to substantially horizontal position, pointing generally in the direction of the pre-selected aiming point. Conventional cross wires are provided at the muzzle, the gun is primed and the cover of feed box 6 is opened.

Standing in front of the trunnion block at the side of the gun barrel, the operator grasps the sight by handle 29. With the open end of tube 9 inclined upwardly, the sight is inserted upwardly through the bottom of trunnion block 1 and moved forwardly until it rests on top of breechblock 8. The rear end of the sight is then swung upwardly until the tube 9 is in alignment with the barrel axis, after which, the tube is slid into the breech. Handle 29 is then rotated clockwise about 5 so that the line of sight clears the cartridge feeder pawl connector shaft. This step can be simplified by looking into the open feed box while inserting the sight. Standing on the left, front side of the top carriage platform, the operator looks downwardly into the feed box and viewsv an image of the two cross wires in mirror 25. The, gun controls are then manipulated until the aiming point and intersection of wires 33 and 34' are centralized within the opening of disc "5. The gun or director sights having been adjusted upon the same aiming point, the proper connections are made and the director may start picking up a target while the breech and muzzle sights are being removed. Removal of the breech sight leaves the gun in primed condition ready for the insertion of a clip of ammunition. Firing can thus begin almost immediately after removal of the bore sights.

I have thus provided a bore sight that is easily and inexpensively built, while being highly accurate. Furthermore, the ease with which it may be applied to a gun, encourages frequent bore sighting and thus makes for greater accuracy. While I haveshown a preferred form of the invention, modifications, alterations and substitutions will occur to those skilled in the art of fire control, especially where a sight embodying the foregoing principles is to be adapted for other types and oalibres of guns. Hence the foregoing disclosure should be taken in an illustrative rather than a limiting sense, and I desire to reserve all such changes as fall within the scope of the subjoined claim.

Having now fully disclosed the invention, what I claim and desire to secure by Letters Patent is:

A bore sight fora gun comprising a cylindrical tube smoothly fitting the breech chamber of said gun and having an open forward end and an inwardly flanged rear end, said inwardly-extending flange defining a circular central opening concentric of the central longitudinal axis of said tube, a hollow elongated casing square in cross section and having its forward edges rigidly secured to said flanged rear end, to secure said casing in coaxial relation with said tube, said casing having a plate inclined at 45 to and extending across said axis, a mirror secured to the outer face of said plate, a peep sight, cross wires each secured at its inner end to respective peripherally spaced points on said peep sight and at their outer ends to peripherally spaced points on said tube to rigidly mount said peep sight in said tube with its sighting aperture coincident with the central axis of said tube, there being an opening in the side of said casing immediately rearwardly of said tube through which an image of said peep sight may be viewed in said mirror along a line normal to said axis, and a handle secured to said casing and extending generally oppositely and parallel to said line.

HAROLD O. JOHNSON.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 399,286 Russell Mar. 12, 1889 793,131 Henkes June 27, 1905 893,836 Czapski July 21, 1908 962,175 Straubel June 21, 1910 1,329,366 Careaga Feb. 3, 1920 2,294,913 Kaufman et a1 Sept. 8, 1942 2,308,635 Walker June 19, 1943 

